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Cecie Starr Christine Evers Lisa Starr www.cengage.com/biology/starr Chapter 41 Community Ecology (Sections 41.1 - 41.5) Albia Dugger • Miami Dade College 41.2 Community Structure • Symbiosis (“living together”) refers to a relationship in which two species have a prolonged close association • Two species that interact closely for generations can coevolve – an evolutionary process in which each species acts as a selective agent on the other • symbiosis • One species lives in or on another in a commensal, mutualistic, or parasitic relationship Species Interactions • Species interactions can be mutually beneficial, mutually harmful, or benefit one species while harming the other • Example: Commensal ferns attached to the trunk of a tree; the fern benefits from the light, and the tree is unaffected • commensalism • Species interaction that benefits one species and neither helps nor harms the other Commensalism • A tree with a commensal fern • The fern benefits by growing on the tree, which is unaffected by the presence of the fern 41.3 Mutualism • In a mutualistic interaction, two species benefit by taking advantage of one another • Example: Pollinators eat nectar and pollen, and plants receive pollen from other plants of the same species • mutualism • Species interaction that benefits both species Mutualism and Defense • For some mutualists, the main benefit is defense • Example: Sea anemone and anemone fish • An anemone fish has a mucus layer that shields it from stinging cells (nematocysts) of a sea anemone • Tentacles of the anemone protect the fish from predators • The anemone fish chases away the few fishes that are able to eat sea anemone tentacles Sea Anemone and Anemone Fish 41.4 Competitive Interactions • Each species has an ecological niche defined by physical and biological factors; the more similar the niches of two species are, the more intensely they will compete • An animal’s niches include the temperature range it can tolerate, species it eats, and places it can breed • A flowering plant’s niche would include its soil, water, light, and pollinator requirements • ecological niche • All of a species’ requirements and roles in an ecosystem Effects of Competition • Species compete most intensely when a shared resource is the main limiting factor for both • Whenever two species require the same limited resource to survive or reproduce, the better competitor will drive the less competitive species to extinction in that habitat • competitive exclusion • Process whereby two species compete for a limiting resource, and one drives the other to local extinction Experiment: Competitive Exclusion • EX: with an invasive species • Two Paramecium species compete for the same food (bacteria) • Each species thrives when grown alone • When grown together, P. aurelia drove P. caudatum to extinction Experiment: Competitive Exclusion Experiment: Competitive Exclusion Fig. 41.6.1, p. 695 Experiment: Competitive Exclusion Fig. 41.6.2, p. 695 Experiment: Competitive Exclusion Fig. 41.6.3, p. 695 0 4 8 12 16 20 24 Time (days) 0 P. aurelia alone 4 8 12 16 20 24 Time (days) Relative population density P. caudatum alone Relative population density Relative population density Experiment: Competitive Exclusion 0 Both species together 4 8 12 16 20 24 Time (days) Stepped Art Fig. 41.6, p. 695 ANIMATION: Competitive Exclusion To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Invasive Species • Gypsy moths native to Europe and Asia feed on oaks through much of the United States Invasive Species • Nutrias native to South America are abundant in freshwater marshes of the Gulf States Resource Partitioning • Resource partitioning is an evolutionary process by which species become adapted to use a shared limiting resource in a way that minimizes competition • Example: Three plant species growing in the same field • resource partitioning • Species become adapted in different ways to access different portions of a limited resource • Allows species with similar needs to coexist Resource Partitioning • Roots of each species take up water and mineral ions from a different soil depth • Reduces competition among the species and allows them to coexist ANIMATION: Resource Partitioning To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 41.6 Parasites, Brood Parasites, and Parasitoids • Some plants and animals benefit by withdrawing nutrients from other species • Some species trick others into providing parental care Parasitism • With parasitism, one species (the parasite) feeds on another (the host), without immediately killing it • Endoparasites live and feed inside their host • Ectoparasites feed while attached to a host’s external surface • parasitism • Relationship in which one species withdraws nutrients from another species, without immediately killing it 41.1 Fighting Foreign Fire Ants – Biological Controls • NOT 41.6 BUT SUPPORTIVE STORY FROM 41.1: • Red imported fire ants, Solenopsis invicta, have a venomous sting, disrupt native wildlife communities, and are not controlled by pesticides • Biological control involves phorid flies, specialized parasites (parasitoids) that kill their host by laying an egg in the ant’s tissues – the larvae eats its way through the fire ant and undergoes metamorphosis in its head • community • All species that live in a particular region Phorid Fly and Fire Ant • Phorid flies insert a fertilized egg into an ant’s thorax • Parasitized ant that lost its head after a developing fly larva moved into it Fighting Foreign Fire Ants (revisited) • Red imported fire ants (RIFAs) did not evolve in North America, so there are few predators, parasites, or pathogens to hold them in check • Global climate change is expected to help RIFAs extend their range in the US ANIMATION: Succession To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE 41.7 Ecological Succession • Species often alter the habitat in ways that allow other species to replace them (ecological succession) • The first, opportunistic colonizers of new or newly vacated habitats are pioneer species, which have high dispersal rates, grow and mature fast, and produce many offspring • pioneer species • Species that can colonize a new habitat • Mosses, lichens, some flowering annuals Primary Succession • Primary succession begins when pioneer species colonize a barren habitat with no soil, such as a new volcanic island or land exposed by the retreat of a glacier • Pioneers help build and improve the soil • primary succession • A new community becomes established in an area where there was previously no soil Primary Succession Secondary Succession • In secondary succession, a disturbed area within a community recovers. • Occurs in abandoned agricultural fields and burned forests • secondary succession • A new community develops in a site where the soil that supported an old community remains